(a) Field of the Invention
The present invention relates to a liquid crystal display (LCD), a driving device thereof, a digital to analog (D/A) converter, and an output voltage amplifying circuit.
(b) Description of the Related Art
Recently, as personal computers and televisions have been become lighter and slimmer, display devices have also been required to become lighter and slimmer, and flat displays such as liquid crystal displays (LCD) other than cathode ray tubes (CRT) have been increasingly researched according to the requirements.
The liquid crystal display (LCD) is a display device for acquiring a desired video signal by applying an electric field to a liquid crystal material having an anisotropic dielectric constant and injected between two substrates, controlling the intensity of the electric field, and controlling the light transmitted to the substrates from an external light source (a back light).
The liquid crystal display (LCD) is representative of the portable flat panel displays, and a thin film transistor liquid crystal display (TFT-LCD) using a thin film transistor (TFT) as a switch is mainly used.
In general, the liquid crystal display (LCD) uses a decoder for outputting a voltage corresponding to input digital data in order to select a gray voltage corresponding to a grayscale to be displayed through a pixel of a liquid crystal display (LCD) panel from among a plurality of gray voltages generated based on a reference gray voltage.
FIG. 1 shows a brief general decoder for outputting a voltage corresponding to 10-bit input digital data.
As shown in FIG. 1, a general decoder for outputting a voltage corresponding to 10-bit input digital data includes 2046 (=211−2=210+29+28+27+26+25+24+23+22+21) switches. When the digital data are increased by one bit, the decoder must include 4094 (=212−2) switches. The increased number of switches included in the decoder corresponding to the bit number of digital data increases the cost of realizing the liquid crystal display (LCD) and the area of realizing the liquid crystal display (LCD).
Korean Patent No. 10-0336683 discloses a skill for reducing the switches included in the conventional decoder. Korean Patent No. 10-0336683 changes the structure of an output amplifier for outputting a gray voltage to combine the voltages and outputs all voltages corresponding to the input digital data rather than reducing the number of switches included in the decoder, which will be described with reference to FIG. 2.
FIG. 2 shows a conventional output amplifier structure.
The output amplifier according to Korean Patent No. 10-0336683 shown in FIG. 2 includes input transistors (S1, S2, S3, S4) driven by a plurality of voltages (Va, Vb, Vc, Vd) output by the decoder and coupled in parallel to form a first input terminal, and input transistors (S1′, S2′, S3′, S4′) driven by a feedback signal (Vx) corresponding to an output voltage (Vout) and coupled in parallel to form a second input terminal. One terminal of each input transistor (S1, S2, S3, S4) forming the first input terminal and each input transistor (S1′, S2′, S3′, S4′) forming the second input terminal is coupled to a single node (Na), and the node (Na) is coupled to the power source (VSS) for supplying the VSS voltage through a constant current source (Ix).
However, the output amplifier shown in FIG. 2 cannot accurately reflect the voltage difference of a plurality of voltages (Va, Vb, Vc, Vd), and hence, a supplementing method is required.